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DAC3482 Different OIP3 between channels?

Sefa Tanis
Prodigy 65 points

Other Parts Discussed in Thread: DAC3482, DAC3484

On the Spectrum Analyzer one channel has a -15 dBm per tone fund output and 86 dBc IMD products.

The other channel has a -15 dBm per tone output and 70 dBc IMD products. 

Is this an expected behaviour between channels?

Or what could I be doing wrong?

Each arm of the DAC3482 output is terminated with 50 ohm resistors, together with shunt 390nH pull down inductors. There are 100pF DC blocking caps at each output port.

DAC Rate=1228.8Msps

Mixer ON, NCO=OFF.

Two tone output 5 MHz separation 180&185 MHz

4x Interpolation

0 dBFS

QMC=OFF

Thanks in advance.

Sefa

  • 0
    TI__Guru* 83035 points

    Sefa,

    Your termination appears to be correct. I believe you had referred to the DAC348x interface app note published on the web. The common mode is set at 0V. You may want to check your AC swing to make sure it is still within the compliance voltage. 

    http://www.ti.com/litv/pdf/slua647a

    I believe these are the channel-to-channel variations of the different DAC output channels. If you look at the DAC3482 datasheet, Figure 15 (IMD3 performance vs. input digital scale), you will notice that the typical IMD performance of the DAC3482 at -12dBFS, 180MHz IF is about 75dBc. This plot is taken after characterization of 5 to 10 units, and we picked one of the units to demonstrate the typical characteristics of the DAC. The purpose for this is to give our customer to most conservative and most accurate view of the DAC348x device performance.

    To give you an idea of the typical channel-to-channel variations, our characterization engineer had provided the IMD3 performance vs. input digital scale of the 4-channel DAC3484 device. You can see that at 160MHz IF, the channel B shows about 88dBc of IMD3 at -12dBFS input, while other channels exhibits about 75dBc of IMD3. 

    -Kang

    DAC3484_MRQFN_IMD3_vs_Input_Scale_1250MSPS.xls